The present invention relates generally to game balls and more particularly is directed to game balls having a hollow central core for use in playing baseball and softball.
Professional and competitive play game balls such as baseballs and softballs are traditionally constructed with a solid, spherical central core formed of cork, kapok, or other similar material, surrounded by windings of thread or yarn, and covered with a stitched-on leather cover. These traditionally constructed game balls typically possess excellent play characteristics, particularly when they are new. However, they are also relatively expensive and thus are rarely used outside high levels of game play.
In spite of the expense and the care that goes into manufacturing, balls having a traditional construction often have a very limited playing life. Striking a ball with a bat in the normal course of play often causes the surface of the ball to become flattened at the point of impact, or to otherwise depart from its original spherical shape. Forces from the impact between the ball and bat also travel through the ball and contribute to the breakdown and destruction of the central core. A ball with traditional construction that receives repeated bat impacts may loose much of its liveliness as the central core deteriorates. Therefore, baseballs of traditional construction are often removed from play in professional and high level competitive play after relatively little use.
An additional problem associated with balls having a central core of cork or kapok resides in variation of the core density. As cork and kapok are naturally occurring materials, little can be done to control their density. It will be appreciated that core densities which are significantly out of average will contribute to a ball falling outside of acceptable weight range limits and may cause the ball to have non-standard performance. Therefore, central cores made of cork and kapok are subject to rejection due to wide variations in density. Naturally, this contributes to increasing the expense of the finished game ball.
A further problem associated with a baseball or softball of traditional construction resides in the physical distribution of the ball""s mass within the structure of the ball. The traditional solid central core centralizes the mass of the ball, resulting in a lower moment of inertia when compared to a ball having its mass distributed nearer its exterior surface. A lower moment of inertia manifests itself in certain aspects of ball performance such as a higher spin rate and an increased influence from Magnus effect. The net effect of higher spin rates and increased Magnus effect makes such a ball tend to fly higher and/or curve more strongly in flight. For play in confined areas or for use as a xe2x80x9ctraining ballxe2x80x9d by less skilled players, a ball with a higher moment of inertia and consequently, lower spin rate and less Magnus effect influence is preferred.
It is therefore a goal of sporting goods manufacturers to develop game balls, such as baseballs and softballs, which have the look, feel and handling characteristics of traditional game balls but which are economical for the consumer to use and are highly durable. In addition, it is a goal of sporting goods manufacturers to develop such game balls which have play characteristics including lower spin rate and lower influence from Magnus effect. To this end a number of balls have been developed wherein the traditional central core materials of cork and kapok are replaced with various non-traditional materials, the central core has new configurations or in some balls, the windings are eliminated.
U.S. Pat. No. 5,035,425 discloses a non-regulation light weight play ball comprising a spherical shell of high density elastomeric polyurethane material wherein the shell has a wall thickness believed to be sufficient to return the shell to its original shape following deformation from bat impact. The central core may be hollow or optionally filled with a low-density foam. Preferably, the shell has a thickness in the range of {fraction (1/16)} to xc2xc inch (approximately 1.60-6.41 mm).
U.S. Pat. No. 4,610,071 relates to a method of making a game ball, such as a baseball or softball. The method includes forming two hemispherical shells of a polyolefin material, placing within the hemispherical shells chemicals which, when they react, expand to form a plastic foam material. The two hemispherical shells are welded together and the foaming materials react to fill the hollow central core within the welded hemispheres with a plastic foam. A cover may then be sewn in place over the core structure.
U.S. Pat. No. 4,880,233 discloses a game ball that is both lighter and softer than regulation game balls. The game ball of the ""233 patent is comprised of a resilient, central core tightly enclosed within a durable cover. The core is formed from two hemispherical shells molded from a rubber-based compound. The hemispherical shells define a hollow central core that may optionally be pressurized relative to the ambient atmospheric pressure in order to impart specific desired rebound characteristics to the game ball. The composition of the core includes 30-40 wt. % of a styrene butadiene rubber, 16-20 wt. % natural rubber, 33-37 wt. % calcium carbonate, and 5-9 wt. % silica powder.
U.S. Pat. No. 4,861,028 discloses a softball comprising a hollow spherical central core and a leather cover which surrounds the core. The spherical core is molded from a mixture of low-density polyethylene and ethylene acid copolymer resin. The ""028 patent discloses that a desired coefficient of restitution of about 0.47-0.52 for the ball may be obtained when the core comprises 40-90 weight percent low density polyethylene and 10-60 weight percent of ethylene acid copolymer. The spherical core disclosed is preferably manufactured using conventional rotational molding techniques.
While the hollow balls previously known in the art may have a higher moment of inertia than do baseballs and softballs of traditional construction, they often tend to xe2x80x9coil canxe2x80x9d or become permanently dented upon making solid striking contact with a baseball bat. Balls having a foamed core, as in U.S. Pat. Nos. 4,610,071 and 5,035,425, tend to resist permanent dents better than hollow core balls due to the structural support provided by the foam. However, a foamed core typically tends to concentrate mass toward the ball""s center, lower moment of inertia and thus increase the rate of spin and Magnus effect influence, both of which are preferably avoided in a ball intended for play in a confined area or for a ball to be used by less skilled players.
An object of the invention is to provide a game ball with a center core having a hollow cavity which is resistant to permanent deformation or damage from making striking contact with a bat.
Another object of the present invention is to provide a game ball having the look and feel of a softball of traditional construction, but which has a hollow central core.
A further object of the present invention is to provide a game ball, such as a softball, which is less costly to manufacture than a game ball made using traditional construction techniques, yet retains the look and feel of a traditional softball.
A still further object of the present invention is to provide a game ball having a higher moment of inertia compared to a softball of traditional construction.
Other objects will be in part obvious and in part pointed out more in detail hereinafter. These and related objects are achieved by providing a game ball with a core defining a hollow central cavity. The core is preferably spherical in shape. The core is formed of a thermoset elastomeric material which, after molding and curing, may be characterized as a hard, rubber-like substance. The combination of the hard elastomeric material, selected for its physical properties, and the thickness of the core walls provide a ball which is less likely to xe2x80x9coil canxe2x80x9d or otherwise be dented on making striking contact with a bat in the normal course of play. The use of a thermoset elastomeric material for the core also reduces the manufacturing cost of the ball compared to traditionally constructed game balls. Also, the thermoset elastomeric core material makes control of core density and overall ball weight much easier than in a ball with a natural material core. In addition, the hollow central cavity of the core raises the game ball moment of inertia compared to a solid center game ball, thereby providing desired performance properties.
A cover overlies the core. The cover may be comprised of natural leather, synthetic leather or other material sewn tightly around the core. Alternately, the cover may be molded on or may be a coating or polymeric skin formed over the core. The outer surface of the core may also form the cover of the ball.
In another embodiment, the inventive game ball may feature a core formed of multiple layers of material. In such a ball the outermost layer is preferably softer than the inner layer or layers of the core. The central cavity of the ball is hollow.
In yet another embodiment of the invention, the central cavity of the ball remains hollow, however the material from which the core is formed is at least partially cellular. The result is a core of thermoset elastomeric material wherein the density of the material and/or softness of the core or a portion of the core may be adjusted by adjusting the degree of xe2x80x9cblowingxe2x80x9d. The cellular materials are of particular utility in combination with a multiple layered core embodiment of the invention.
A better understanding of the invention will be obtained from the following detailed disclosure of the article and the desired features, properties, characteristics, and the relation of the elements as well as the process steps, one with respect to each of the others, as set forth and exemplified in the description and illustrative embodiments.